Gas turbine rotor blades can include blade shroud segments in order to control and minimize leakage flow between the blade tips and the surrounding stator as well as to limit vibration amplitudes. A blade shroud segment can include a platform extending in a plane essentially parallel to the stator opposite to the blade tip and one or more fins, which extend circumferentially and radially outward toward the stator.
The platform of a blade shroud segment can be shaped such that its edges are parallel to those of an adjacent blade shroud platform. In order to withstand the high thermal load during gas turbine operation the blade shroud can be cooled by a cooling fluid (for example, cooling air) passing through a cooling system within the platform of the shroud that is fluidly connected to a hollow interior of a blade airfoil.
The shroud lifetime can be limited by mechanical stresses caused, for example, by centrifugal forces. Such stresses can be reduced by minimizing a wall thickness of the platform, also known as a shroud web. However, a blade shroud segment with a thin wall thickness may not line up with the blade shroud segment of an adjacent blade due to manufacturing and assembly tolerances, which can occur even if the tolerances are kept at a minimum.
A further mismatch can result from deformations of the shroud platform during turbine operation due to thermal and mechanical loading. A mismatch between two adjacent blade shroud segments can allow hot gas to enter the cavity between the stator and the blade shroud. The shroud can be designed with materials having a creep resistance and oxidation resistance up to a temperature less than a temperature of the hot gas. Hot gas ingestion therefore can cause premature failure of the shroud and the adjacent static and moving components.
EP-A1-1 591 625 discloses a gas turbine blade with a shroud segment which includes a platform extending, for example, in a plane essentially matching a contour of a stator opposite a blade tip, and side rails that extend radially and along one or both edges of a platform that faces a platform of an adjacent gas turbine blade shroud segment.
An increase of a wall thickness can result in an increase of the stiffness of a component according to a third power of the wall thickness. The blade shroud segment of EP-A1-1 591 625 has an increased wall thickness that is limited to side regions of the platform. Thus, the benefits of increased stiffness can be achieved with a resulting decrease in deformation and bending in the radial outward direction and increased time of turbine operation. The increase in wall thickness can be localized such that it causes no significant increase in the mass of the shroud segment and no significant increase of the mechanical loading.
However, in known shroud segments there is either no side rail or a constant height side rail. The disclosure relates to geometry of the side rails for blade shroud segment coupling which can provide simplified manufacturing, minimization of hot gas ingestion, improved stiffness and improved shroud cooling.